For years, scientists, advocates and political leaders across the globe have pointed to a “two degrees Celsius” rise in global average temperature as the threshold for dangerous climate change. Now, with this threshold fast approaching, the scientific and policy communities are beginning to look seriously at what the world will look like if we reach a four-degree Celsius rise. And the picture is not pretty.

A new report released today by the World Bank, "Turn Down The Heat: Why a 4°C Warmer World Must be Avoided," warns of the escalating dangers of the world hitting a four-degree rise in global temperature.

"Lack of action on climate change threatens to make the world our children inherit a completely different world than we are living in today," said World Bank Group President Jim Yong Kim. "Climate change is one of the single biggest challenges facing development, and we need to assume the moral responsibility to take action on behalf of future generations, especially the poorest."

The four-degree mark is approaching quickly. The World Bank report states that "even with the current mitigation commitments and pledges fully implemented, there is roughly a 20 percent likelihood of exceeding 4°C by 2100." However, this could be much sooner if the carbon-cycle feedbacks are strong.

"Feedbacks" refer to changes that result from warming that could lead to even more warming. For example, as the temperatures rise and the Arctic permafrost melts, large amounts of methane, a powerful heat-trapping gas, could be released into the atmosphere and accelerate warming.

Feedbacks cause much of the uncertainty in climate projections and are at the heart of what scientists fear most. As explained in a recent article published in the Philosophical Transactions of the Royal Society, if feedbacks are strong, then four-degree Celsius warming could be reached by the early 2060s.

The World Bank report comes at a critical time when public discussion about the climate crisis has been reignited in the aftermath of superstorm Sandy. As communities across the storm-struck coastlines clean up and rebuild, we must also rethink how we build, where we build, and what levels of risk we will accept.

As award-winning author Naomi Klein explains in her book The Shock Doctrine, we have become addicted to extreme risk in finding new energy and new financial instruments. And the result is that too often, we're left to clean up a mess afterward.

In the case of climate change, we will mostly be leaving the mess to our children.

As we move beyond the two-degree threshold, we need to understand as a community what this means and assess if we are prepared to accept this level of risk for our children. As Kofi Annan, Former Secretary-General of the United Nations, has asked: "Do we really wish to leave future generations with a world of deadly droughts, flooded coastal cities, and the loss of priceless biodiversity, including coral reefs?"

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